Field of the Invention
The present invention relates to an apparatus and method of manufacturing silicon seed rod in which two silicon seeds are joined into one long silicon seed rod by mechanical coupling.
Description of Related Art
As a polycrystalline silicon producing method, a method of producing by the Siemens method has been known. According to this producing method by the Siemens method; a plurality of silicon seed rods are provided in a reactor and heated, raw material gas including chlorosilane gas and hydrogen gas is supplied to the reactor to bring the raw material gas into contact with the heated silicon seed rods, and polycrystalline silicon is deposited on the surfaces of the silicon seed rods by heat decomposition and hydrogen reduction of the raw material gas as columnar-shaped silicon rods. In this case, the silicon seed rods fixed upright on electrodes mounted on a bottom plate portion of the reactor. Every two silicon seed rods are paired and the upper end portions thereof are connected to each other by a short connecting rod or bridge so that they are formed in a H-shape.
In the producing method of polycrystalline silicon by the Siemens method, the silicon seed rods are manufactured by cutting manufactured silicon rods into silicon seed rods. Since the upper parts of the silicon rods, which are connected by the connecting rods, are cut off when separating in order to be taken out from the reactor, the silicon seed rods are shorter than the original silicon seed rods. There is about 100 mm of length of seed rod lost every time a rod is harvested. This 100 mm comes from the approximately 60 mm of seed rod in the electrode and 40 mm of seed rod above the electrode which is removed because of carbon contamination. Therefore, since the silicon seed rods are getting shorter every manufacturing and cutting out, it is necessary to manufacture new silicon seed rods from silicon rods or to make silicon seed rods from existing long silicon seed rods, periodically. Long silicon seed rod can be produced, for example, by joining short silicon seed rods as described in Japanese Unexamined Patent Application, First Publication No. S63-242339.
Japanese Unexamined Patent Application, First Publication No. S63-242339 describes below a welding method for making silicon seed rods. First, two silicon seed rods are inserted in a horizontal heating tube and are fixed in a state in which the rods are abutted. Next, a heating tube is arranged vertically; a preheating ring is heated into glowing state by a high-frequency heating coil disposed in the heating tube; and one of the silicon seed rods is preheated. After preheating the silicon seed rod, the high-frequency heating coil is moved to the abutted portion of the two silicon seed rods so as to heat the abutted portion, so that the abutted portion is melted by further raising the heating output. After that, by decreasing the output of the high-frequency heating coil so as to cool down the abutted portion of the silicon seed rods, the silicon seed rods are welded. This is the standard way in which two shorter seed rods are joined to form one long seed rod. Welding rods together takes considerable time and energy.